In recent years, for the purpose of energy saving and downsizing, light emitting diodes (hereinafter also referred to as “LEDs”) are used as light sources for lighting. Light emitting devices each having a combination of an LED and a light flux controlling member (lens) for controlling distribution of light emitted from the LED are used in place of, for example, fluorescent lighting and halogen lamps. Further, direct surface light source devices incorporating the light emitting devices in a lattice shape are used as a backlight in transmission type image display devices, such as liquid crystal display apparatuses (refer to, for example, PTL 1).
FIG. 1 is a schematic plan view illustrating the configuration of surface light source device 10 described in PTL 1. In FIG. 1, an optical sheet (e.g., a diffusion plate) disposed on the front is omitted. As illustrated in FIG. 1, surface light source device 10 described in PTL 1 includes support board 20, circuit boards 30 fixed on support board 20, light emitting diodes 40 respectively mounted on circuit boards 30, reflective sheet 50 which is disposed on support board 20 and circuit boards 30 and which includes holes 52 respectively provided at positions corresponding to light emitting diodes 40, lenses 60 respectively disposed above light emitting diodes 40, and an optical sheet (not illustrated) disposed above lenses 60. Hole 52 in reflective sheet 50 has a diameter larger than that of lens 60, and lens 60 is fixed on circuit board 30 which is exposed via hole 52 of reflective sheet 50. Each lens 60 also includes protrusion 62 that protrudes toward the outside from the outer peripheral portion of lens 60. Protrusion 62 is formed to extend over the edge of hole 52 so as to face a part of reflective sheet 50. In surface light source device 10 described in PTL 1, as protrusions 62 of lenses 60 are placed on reflective sheet 50, separation of reflective sheet 50 from support board 20 can be prevented.
Lens 60 including protrusion 62 is more likely to generate luminance unevenness compared to lens 60 including no protrusion 62. In surface light source device 10 described in PTL 1, lenses 60 are disposed in such a manner that respective protrusions 62 are directed in different directions. This configuration may be able to reduce the luminance unevenness caused by protrusions 62. In the example illustrated in FIG. 1, lenses 60 are fixed so that each protrusion 62 faces the side among the four sides of support board 20, which is closest to lens 60.